But if that seems bad enough, imagine our temperatures plummeting to such bone-aching lows that British rivers freeze for months at a time.

Our streets would become impassable ice sheets, industry would grind to a halt, vital supplies would be stranded, hospitals overwhelmed and power supplies fail under the unprecedented demand.

Similarly lethal chaos has occurred before, in the harshest period of a centuries-long European cold snap called the Little Ice Age.

Between the 17th and early 19th centuries, average temperatures dropped by two degrees centigrade and our winters became so vicious the Thames froze utterly on seven occasions.

With its major river blocked, London’s commerce stalled. In the city and surrounding countryside, thousands of people died. Farm animals were wiped out. The wind was even cold enough to crack tree trunks.
So far, so historical. And given the relentless 21st-century warnings that the ice even at the earth’s poles is melting, one could be forgiven for thinking that such conditions will never be seen again in Britain.

Except that a professor of mathematics at Northumbria University is warning that history is in imminent danger of repeating itself.

And Valentina Zharkova is not alone in that startling view. She is part of an international collaboration of academics in the UK and Russia who have sparked controversy by warning that the world could be plunged into another ‘mini ice age’ in a little over a decade.

The thesis is that this could go some way to replicating a phenomenon known as the ‘Maunder Minimum’, after the British husband and wife astronomers, Walter and Annie Maunder, who worked at the Royal Observatory in Greenwich.

In 1895, the pair published a paper reporting a link between sunspots and the Little Ice Age’s coldest period.

Temperatures will start dropping in 2021, according to a mathematical model of the Sun's magnetic energy. In 2011 this image was captured showing an almost clear sun - which experts say could happen for almost a decade from 2030

Professor Zharkova and her team have created a mathematical model which predicts that the Sun’s energy output (in the form of electromagnetic radiation) is about to fall significantly, causing temperatures on Earth to drop.

The fall is caused by changes in the Sun’s internal magnetic fields, which create energy waves in a similar manner to an electric dynamo. One field is in a layer close to the surface, while the other is deep inside.

During an 11-year timespan, the magnetic fields alter cyclically. Professor Zharkova’s team has used data on previous cycles to predict that the dynamo effect in the coming cycles is about to produce a marked drop in radiant heat output from the sun, between the years 2020 and 2050.

The visible evidence for this occurring would be a dramatic reduction in the number of sunspots. These are areas on the sun’s surface that appear cooler — and therefore darker — than the rest of the surface surrounding them.

If the sun’s surface generally cools, then these areas don’t stand out. This same phenomenon was observed during the very harshest period of the Little Ice Age, between 1645 and 1700.

Throughout this time, there were only about 50 sunspots on the surface of the Sun instead of the usual 40,000-50,000.

Professor Zharkova, who has a PhD in Astrophysics, first mooted the idea two years ago, sparking a furious row in the scientific community over the veracity of her claims. Now a new paper, published last year in Astronomy & Geophysics, has reinforced those earlier findings.

She claims that her team’s results are ‘97 per cent accurate’. She describes the research as ‘the first serious prediction of a reduction of solar activity that might affect human lives’.

Previously a mini ice age it hit between 1646 and 1715, even causing London's River Thames to freeze over (pictured)

She adds: ‘I am absolutely confident in our research. It has good mathematical background and reliable data, which has been handled correctly . . . as evidence of an upcoming Maunder Minimum.’

Professor Zharkova’s evidence has prompted pundits to predict that, if the sun does indeed turn down its thermostat, then global warming’s effects may be slowed, stopped or radically reversed.

If that is true, the world could indeed witness a return to some kind of ‘mini ice-age’ in which the great rivers of Europe again freeze, temperatures fall by two degrees centigrade or more, and fierce winters grip Britain and mainland Europe with lethal results.

But other leading experts are queueing up to dismiss such fears. Gavin Schmidt, the director of Nasa’s Goddard Institute for Space Studies, is particularly forthright. ‘It’s complete garbage,’ he told reporters.

Many critics argue that, while the Maunder Minimum may have had an effect on past climate, it was far from solely responsible for the Little Ice Age of the 17th and 18th centuries.

Michael Brown, an associate professor of astronomy at Monash University in Australia, points out that ‘The Little Ice Age began before the Maunder Minimum and may have had multiple causes, including volcanism [volcanic activity].’

Indeed, volcanic eruptions around the world seem to have been more frequent after the year 1500 than during the medieval warm period that preceded it. Soot and lava propelled high in the atmosphere can shield the Earth from solar rays, causing significant cooling.

Such powerful effects were seen from the 1815 eruption of Indonesia’s Tambora volcano, one of the most violent ever recorded.

This led to 1816 being dubbed the ‘year without a summer’ — one of the coldest on record, which brought crop failures and starvation to Northern Europe.

Professor Brown adds that numerous scientists have investigated exactly how much the Maunder Minimum actually reduced the levels of solar energy hitting Earth.

He argues that even the lowest estimated levels would not significantly reverse the effects of modern climate change.

‘There is 40 per cent more of the greenhouse gas carbon dioxide in the air now than during the 17th century, and global temperature records are being smashed,’ he claims. ‘A new Maunder Minimum would slow climate change, but it is not enough to stop it.’

Professor Zharkova is unimpressed by such arguments. The new drop in sunspots might bring another mini ice age, she believes. On the other hand, she says, it might be beneficial — as it could simply halt or slightly reverse the effects of climate change, giving the world’s leaders precious extra time in which to act.

‘I hope global warming will be overridden by this effect, giving humankind and the Earth 30 years to sort out our pollution,’ she suggests. After that, she predicts, any positive impact on global warming will disappear when the sun’s magnetic waves revert to their normal pattern in the 2050s.

Who to believe? Given that we can’t even trust our highest-paid forecasters to get tomorrow’s weather right, we might be best flipping a coin to decide.

But here is a much safer prediction. The Thames won’t freeze over in London again. This is because controversies such as sunspots and global warming won’t have the casting vote. It all comes down to engineering. And that means no more ice fairs.

Back in the Little Ice Age, the medieval London Bridge was constructed with many small arches on numerous piers, with weirs in between. During winter, pieces of ice would get lodged between the piers and effectively dam the river, making it comparatively easy to freeze over.

That’s why seven major ‘frost fairs’ were held between 1607 and 1814, when the Thames turned to ice for up to two months at time.

So thickly frozen was the ice that you could roast cattle upon it. Mutton was served in slices soused liberally with alcohol.

Even royalty joined in. Charles II enjoyed a spit-roasted ox at the Blanket Fair of 1684, during the notorious Great Winter, when even the seas of southern Britain were said to have frozen solid for up to two miles from shore.

With each new frost fair, stallholders vied to create ever-more spectacular attractions. In 1814, at the last great fair, the printer George Davis constructed a press on which he published his 124-page book, Frostiana; Or A History Of The River Thames In A Frozen State.

Further upstream, at Blackfriars, a full-grown elephant was paraded across the ice.

But the medieval London Bridge was demolished in 1831. And from the mid-1800s, engineers began building embankments along the London Thames, speeding the river’s flow significantly. All of which means it moves too quickly to freeze over nowadays.

But while there’s no need to get your ice skates on, the return of the Maunder Minimum could ensure that we still get to enjoy romantically snowy Christmases and New Years — for the next few decades at least.